The present invention relates to implantable medical devices, and more particularly to an implantable microminiature stimulator (or “microstimulator”) or microminiature sensor (or “microsensor”) comprising a microdevice and one or more remote electrodes adapted to attach to one or more muscle or nerve fibers (or muscles or nerves) and to electrically stimulate the muscle or nerve at the point of attachment in a controlled manner, or to sense one or more specific parameters that originate at or near the point of attachment. More particularly, the invention relates to an implantable microstimulator and/or microsensor (hereafter referred to as a “microdevice” or “microdevices”) having a lead connecting one or more remote electrodes to the microdevice for stimulating or sensing.
Neurological disorders are often caused by neural impulses failing to reach their natural destination in otherwise functional body systems. Local nerves and muscles may function, but, for various reasons, injury, stroke, or other cause, the stimulating nerve signals do not reach their natural destination. For example, paraplegics and quadriplegics have intact nerves and muscles and only lack the brain-to-nerve link, which stimulates the muscles into action.
Prosthetic devices have been used for some time to provide electrical stimulation to excite muscles, nerves or other tissues. Such devices vary in size and complexity. For example, some systems comprise large, bulky systems feeding electrical pulses by conductors passing through the skin. However, complications, including the possibility of infection, arise in the use of muscle, nerve or other stimulators which have conductors extending through the skin or which have nerve-stimulating electrodes that puncture or penetrate the epineurium.
Small, implanted stimulators are also known in the art which are controlled through telemetry signals, such as are discussed in U.S. Pat. No. 4,524,774 (invented by Hildebrandt). However, in the use of implanted stimulators, difficulties arise in providing suitable, operable stimulators which are small in size and have the capability to receive and store sufficient energy and control information to satisfactorily operate them without direct connection. Hence, what is needed is an implantable stimulator that avoids the use of through-the-skin conductors, epineurium-penetrating electrodes, or other tissue-penetrating electrodes, and is small enough to facilitate easy implantation, yet has sufficient capacity to receive and store energy and control information so as to provide useful muscle or nerve stimulation.
The microdevices described in U.S. Pat. Nos. 5,193,539 and 5,358,514 comprise miniature devices that both receive power and control signals inductively from sources outside the body and provide stimulation or sense signals to muscles and nerves touching the device. Unfortunately, the muscle or nerve that requires stimulation or sensing is often deep inside the body and very inefficient inductive power transmission results. One solution would be to provide a battery in the microdevice. However this approach is technically difficult and would create a requirement for extensive surgery if it is necessary to remove the system in case of failure or at the end of the battery life. What is needed, therefore, is a way to efficiently power the microdevice and to provide stimulation or sensing in the desired location deep within the body.
Additionally, the microdevices described in U.S. Pat. Nos. 5,193,539 and 5,358,514 require a transmitting coil to be located outside the skin adjacent to the microdevice. In some body locations where an extreme degree of flexing takes place (for example the ankle, knee, or elbow), it would be difficult to easily attach the external coil. What is needed, therefore, is a way to power the microdevice when the electrode must be located in one of these locations.
The present invention advantageously addresses the above and other needs.